This is how I deal with multi Base Url API

GithubIssueHelper.java

package im.ene.lab.whatever.api;

import com.squareup.okhttp.OkHttpClient;

import retrofit.Call;
import retrofit.GsonConverterFactory;
import retrofit.Retrofit;
import retrofit.http.GET;


public class GithubIssueHelper {

  /**
   * The only visible class
   */
  public static class PublicApi {

    public static void register() {
      shoppingApi.register();
    }

    public static void login() {
      meiApi.login();
    }

    public static void getAge() {
      centerApi.setAge();
    }
  }

  private static final OkHttpClient okHttp = new OkHttpClient();  // your http client

  // This is the Shared Retrofit Builder I'm talking about
  private static final Retrofit.Builder retrofitBuilder = new Retrofit.Builder()
      .client(okHttp)
      .addConverterFactory(GsonConverterFactory.create());  // optional

  // Your Base Urls, as many as you want.
  private static final String[] BASE_URLS = {
      "http://shopping.mlm.com", "http://mei.mlm.com", "http://center.mlm.com"
  };

  static {
    // TODO: you may want to do bunch of setup here, shared between Base Urls
  }
  
  /**
   * You have 3 base urls, so we create 3 API interface
   */
  private interface ShoppingApiService {

    @GET("/register") Call<Object> register();
  }

  private interface MeiApiService {

    @GET("/login")
    Call<Object> login();
  }

  private interface CenterApiService {

    @GET("/age")
    Call<Object> setAge();
  }

  /**
   * For your memory. Not necessary. If you have 1000 of them, just use index.
   */
  private static final int SHOPPING_API_INDEX = 0;
  private static final int MEI_API_INDEX = 1;
  private static final int CENTER_API_INDEX = 2;

  /**
   * And 3 API helper instance. All are private, invisible to User
   */
  private static final ShoppingApiService shoppingApi =
      retrofitBuilder.baseUrl(BASE_URLS[/* 0 */ SHOPPING_API_INDEX]).build().create(ShoppingApiService.class);

  private static final MeiApiService meiApi =
      retrofitBuilder.baseUrl(BASE_URLS[/* 1 */ MEI_API_INDEX]).build().create(MeiApiService.class);

  private static final CenterApiService centerApi =
      retrofitBuilder.baseUrl(BASE_URLS[/* 2 */ CENTER_API_INDEX]).build().create(CenterApiService.class);
}

How to use:

Call

GithubIssueHelper.PublicApi.register();

to register.

@eneim Thanks for your help, Finally I take your advice in my project...divide interface is a good technical scheme and it work well in my project....